That's really hard to answer. Probably calculus just because of its applications in physics and real life. But some things like topology and number theory are very interesting, even if they don't have as much of a direct application. I also really love geometry and have been reading Euclid's elements in my free time, it's really interesting to see the proofs for all the things that we were taught in school. Elements is definitely a classic and I would recommend it to anyone, it is not reliant on any equations or system of measurements and that's part of its beauty.
Also, Black Adder was a BBC TV show with Rowan Atkinson, Stephen Fry, Hugh Laurie, and Tony Robinson, it's a funny show.
What is your favorite type of tea?